Re: Problem (bug ?) with RATE and F1 in $PK

From: Leonid Gibiansky <lgibiansky@emmes.com> Subject: Re: [NMusers] Problem (bug ?) with RATE and F1 in $PK Date: Fri, 02 Nov 2001 08:43:36 -0500 I think this is a feature, not a bug. The motivation (at least how I interpreted it when I came across this problem) is the following: bioavailability is treated as some factor outside of the system. F1 affect the input. You may assume that the tablet (or any other drug form) is reduced (multiplied) by F1 at time of dosing. So available amount is NEW_AMT=F1*AMT. This does not affect the rate. That is why attempts to change rate by changing the bioavailability cannot be successful (and this can be seen only by looking on the concentration or rate). Bioavailability is used only once, for the dose record, to multiply amount by F1. To change rate you probably need to assign duration D1 (computed as AMT/RATE). Then any changes in F1 will lead to changes in RATE (NEW_ RATE = NEW_AMT/D1= F1*AMT/ (AMT/RATE) =F1*RATE). Leonid